Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP LTE systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals (e.g., a mobile station), and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single input-single output, multiple input-single output or a multiple-input-multiple-output (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized. For example, a MIMO system can support time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
Today's broadband wireless systems require efficient and powerful hardware, for example, application specific integrated circuits (ASIC), to support high rate data communications and also require highly flexible apparatus to support varied control channels. Data channels usually employ standard modulation techniques, such as quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM) etc. However the control channels, including different pilot channels, require special treatment. Control channels are low throughput in nature but require high reliability. As a result, control channels often use special modulation schemes, irregular and varied tones/orthogonal frequency division multiplex (OFDM) symbols resource allocation, channel specific hopping, and the reuse of tone resources among different channels. Moreover, as part of wireless standard evolution, the control channels are often modified over time. Also the control channel formats between different standards, such as Ultra Mobile Broadband (UMB) and Long Term Evolution (LTE), are very different and flexibility in a system to adapt to one or the other is needed for versatility.